1. Field of the Invention
This invention relates to silver halide photographic materials, more particularly, to improved lith-type photographic materials as well as a development method therefor.
The present invention relates to development methods for exposed, high contrast silver halide photographic materials by the use of an automatic continuous processing apparatus, and the improvements realized by the present invention are primarily increased image contrast and a marked reduction or perfect removal of drag streaks in the resulting developed images.
2. Description of the Prior Art
So-called "lith" type photographic films which are used for the preparation of a printing master usually utilize silver halide photographic emulsions of an extremely contrasty nature. In lith-type photographic materials, the exposed areas exhibit an auto-catalytic activity during development, thus forming an image of extremely high contrast. Developer solutions used for such high contrast photographic films are quite different from those used for ordinary black and white photographic films. Usually, such a high contrast film is quite sensitive to the reaction products in the developer solution, e.g., when such a film is subjected to continuous development (continuous film transport conditions), local shortages or starvation of the principal reducing agent or diffusion of the reaction products caused by development takes place at the areas which are adjacent areas where development (reduction of silver halide) proceeds vigorously.
Hence, when such a film is processed with an automatic processor through which the film is continuously transported (as disclosed in U.S. Pat. Nos. 3,025,779, 3,545,971, 3,573,914, 3,615,524, 3,625,689, 3,678,842, 3,678,843, 3,724,355, etc., hereby incorporated by reference) an image defect tends to appear in the resulting image which has been called "drag streaks" or "directional drag streaks" in film halftone areas.
Drag streaks also appear in high density regions, which, for example, in the case of halftone image reproduction have a dot area of from 50 to 90%, adjacent low density regions, which, for example, have a dot area of 20% or lower.
The formation of such drag streaks in the latter case can be attributed to the fact that the developer solution "dragged into" a high density area from a low density area includes a higher concentration of the principal reducing agent and a lower concentration of the reaction or developer exhaustion products (mainly bromide ion) than the average, and development thus proceeds in an uneven fashion. Further, based on the same mechanism as in drag streak formation, other defects, i.e., dot distortion and dot size variation, are observed in a halftone image in a high contrast film processed with a continuous transportation type automatic processor. These defects are inherent to processing with such an automatic processor, and are not observed when the film is processed in a vat.
As has been hitherto described, though considered to be peculiar to high contrast silver halide photographic materials, drag streak formation is quite similar to the edge effect which is generally observed in ordinary silver halide photographic materials (see The Theory of the Photographic Process by Mees at page 1031, the revised edition). Drag streaks can be regarded as an intensified edge effect, synergistically enhanced by the high contrast of the lith film when processed in a continuous transporting automatic processor. Therefore, in order to reduce or minimize drag streaks of high contrast film processed in a continuous transporting automatic processor, one must take care to:
i. utilize a developer together with a photographic film whose sensitivity does not highly depend on developer fatigue, and
ii. remove reaction product formed by development from the developing system. These conditions can also be deduced from the description in The Theory of the Photographic Process by Mees on 1031, the revised edition.
The elimination or reduction of drag streaks and of dot distortion would be a substantial contribution to the graphic arts.
One technique effective to reduce drag streaks is described in U.S. Pat. No. 3,625,689, according to which drag streaks are effectively prevented in a photographic member having a silver halide photosensitive emulsion comprising at least 85 mol% silver chloride and from 0.1 to 5 mol% silver iodide processed with an automatic processor charged with a developing solution containing a principal reducing agent and a condensation product of a carbonyl bisulfite with an amine. However, the above mentioned photosensitive silver halide emulsion is, according to disclosure of the patent, advantageously processed only with a very restricted sort of developer containing a carbonyl bisulfite/amine condensate.
Another technique is disclosed in U.S. Pat. No. 3,615,524, which, however, utilizes a cadmium compound added to the silver halide photographic material. The cadmium compound diffuses into the developer as well as into the fixer employed when processing such a material. Since cadmium is quite dangerous and is a source of environmental pollution, there is an urgent need to develop a method for drag streak reduction without the use of a cadmium compound.